The curing of thermosetting resin compositions results in irreversible chemical changes, transforming a fusible and soluble material into a composite that is infusible and insoluble through the formation of covalently cross-linked, thermally stable, three-dimensional networks, generally known as “plastics.” Such plastics are widely used to make heat-resistant articles that remain stable at 500 degrees F., for example. Common types include polyurethane, phenolics, melamine-formaldehyde, urea-formaldehyde, and amino resins. The addition of various fillers and other additives to make reinforced plastics is also well known.